Sunday, October 1, 2023

Materials according to ISO standard

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For the technical article below, we will use the Sandvick Coromant company training manual as a source.

The ISO norm divides the groups of standard materials into 6 different types. Each type has unique properties based on machinability and preparations that place different demands on the tool.

materials according to ISO standards

ISO P = Steel

The greatest variety of different types of parts is probably found under the “P”, which covers different industrial sectors. They are usually long-chipping and have a continuous, relatively uniform chip formation flux. The variations usually depend on the carbon content.

  • Low carbon content = tenacious and pasty material.
  • High carbon content = brittle material.

The necessary cutting force and power vary very little.

What is steel?

  • Steel is the largest group in the machining area.
  • The steel can be unquenched or quenched and tempered with a hardness of up to 400 HB.
  • Steel is an alloy whose main component is iron (Fe). It is made by a casting process.
  • Unalloyed steels have a carbon content of less than 0.8% and contain only Fe but no other alloying elements.
  • Alloy steels have carbon content less than 1.7% and alloy elements such as Ni, Cr, Mo, V, W.

Characteristics of machining in ISO P / Steel:

  • Long chipping material.
  • Relatively easy and smooth chip control.
  • Low carbon steel is pasty and requires sharp cutting edges.
  • Specific cutting force kc:1500–3100 N/mm2.
  • The cutting force and power required to machine ISO P materials remain within a limited range.

ISO M = Stainless Steel

It finds much of its application in the processing sector, flanges, tubes, oil and gas, and in the pharmaceutical sector. During the machining, forms a lamellar and irregular chip because the cutting forces are higher than in normal steel. There are various types of stainless steel.

Chip breaking varies depending on alloy properties and heat treatment, from easy chips to chips that are impossible to break.

What is stainless steel?

  • Stainless steels are alloy materials with a minimum of 11–12% chromium.
  • The carbon content is usually low (it can go down to 0.01%).
  • The alloys are mainly Ni (nickel), Mo (molybdenum) and Ti (titanium).
  • The Cr2O3 layer that forms on the surface of the steel makes it resistant to corrosion.

Characteristics of machining in ISO M / Stainless Steel:

  • Long chipping material.
  • Chip control is regular in ferritic and becomes difficult in austenitic and duplex.
  • Specific cutting force: 1800–2850 N/mm2
  • Machining generates high cutting forces, built-up edge, and heat- and mechanical-hardened surfaces.

ISO K = Cast iron

Mainly it deals with parts for automotive, machinery manufacturing and steel production. The chip formation of ISO-K materials varies from almost pulverized chips to long chips. The power required to machine this group of materials is usually low.

It is important to note that there is a big difference between gray cast iron (near powder) and ductile steel which often exhibits chip breaking similar to that of steel.

What is foundry?

  • There are 3 main types of cast iron: gray (GCI), nodular (NCI), and compacted granite (CGI).
  • Cast iron is an Fe-C compound with a relatively high Si content (1–3%).
  • The carbon content is greater than 2%, which is the maximum solubility of C in the austenitic phase.
  • Cr (chromium), Mo (molybdenum), and V (vanadium) form carbides that increase strength and hardness, but reduce machinability.

Characteristics of the machining of the ISO K / Foundry:

  • Short chipping material.
  • Good chip control in all conditions.
  • Specific cutting force: 790–1350 N/mm2.
  • High-speed machining generates abrasive wear.
  • Moderate shear forces.

ISO N = Aluminum

The aerospace industry, aviation and manufacturers of aluminum wheels for the automotive sector are among the main users of this material. Even though they need less power per mm3, due to the high chip removal rate, it is still advisable to calculate the maximum power required.

What is a non-ferrous material (eg aluminum)?

  • This group contains soft non-ferrous metals, with a hardness of less than 130 HB.
  • Aluminum (Al) alloys with less than 22% silicon (Si) represent the largest share.
  • Copper, bronze, brass, plastic, composites such as Kevlar

Characteristics of ISO N / Non-Ferrous machining:

  • Long chip material.
  • Relatively easy chip control, if alloyed.
  • Aluminum (Al) is pasty and requires sharp cutting edges.
  • Specific cutting force: 350–1350 N/mm2.
  • The cutting force and power required to machine ISO N materials remain within a limited range.

ISO S = Heat Resistant Super Alloys

These are materials that are difficult to machine, within the «S» classification, applications linked to the aerospace, gas turbine and power generation sectors can be found.
Although the range is wide, high cutting forces are usually present.

What are heat resistant super alloys?

  • Heat Resistant Super Alloys (HRSA) include a large number of high-alloy materials based on iron, nickel, cobalt or titanium.
    – Fe base: Annealed or solution treated, aged.
    – Ni base: Annealed or solution treated, aged, cast.
    – Co base: Annealed or solution treated, aged, cast iron.
    – titanium alloys.
  • Properties: Higher alloy content (more Co than Ni), which offers better thermal resistance and increases resistance to traction and corrosion.

Machining characteristics of ISO S / Super Heat Resistant Alloys:

  • Long chipping material.
  • Difficult chip control (segmented chip).
  • A negative rake angle is required if ceramic is used and a positive rake angle is required if carbide is used.
  • Specific cutting force: 2400–3100 N/mm2 for HRSA and 1300–1400 N/mm2 for titanium.
  • The cutting forces and the power required are quite high.

ISO H = Hardened Material

Hardened materials classified as “H” can be found in a wide variety of sectors, ranging from automotive to machinery manufacturing or in the mold and die manufacturing segment. They often have a continuous chip, glowing red.

What is hardened material. ex: hardened steel

  • Hardened steel is the smallest group from the point of view of machining.
  • This group includes quenched and tempered steel with hardness >45–65 HRC.
  • However, typical hard part turning is in the 55–68 HRC range.

Machining characteristics of ISO H / Hardened Material:

  • Long chipping material.
  • Regular chip control.
  • A negative rake angle is required.
  • Specific cutting force: 2550–4870 N/mm2.
  • The cutting forces and the power required are quite high.
Relationship between ISO material and chip in machining

Relationship between ISO material and chip in machining

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